The present invention relates to a method and apparatus for regulating the making of holes or perforations in the envelopes of rod-shaped articles which constitute or form part of rod-shaped smokers's products. More particularly, the invention relates to a method and apparatus for automatically varying or changing the combined cross-sectional area of holes or perforations which are formed in finished rod-shaped smokers' products for the purpose of permitting a requisite quantity of cool atmosphere air to mix with tobacco smoke which flows into a smoker's mouth.
It is already known to provide the tubular envelopes of rod-shaped smoker's products, especially plain or filter cigarettes, with perforations which permit cool atmospheric air to mix with the column of tobacco smoke which is drawn into the mouth of a smoker. When the products are filter cigarettes, especially so-called light filter cigarettes, the holes are formed in that portion of the envelope which surrounds or is closely adjacent to the filter mouthpiece. This insures that the holes remain intact during consumption of the major portion of or the entire tobacco-containing part of the product. It is desirable to insure that the envelope will admit a relatively high percentage of cool atmospheric air, and it is equally desirable to insure that the ratio of cool atmospheric air to the ratio of tobacco smoke in the column which reaches the mouth of the smoker will remain constant or will deviate negligibly from a preselected ratio. This ratio can be called the "degree of ventilation".
It is already known to mechanically perforate the envelopes of filter cigarettes or like rod-shaped smokers' products (hereinafter called cigarettes or filter cigarettes for short) by causing the cigarettes to roll along needles or pins which extend from the surface of a cylindrical or flat body. It was also proposed to burn holes into the envelopes of cigarettes by resorting to spark discharge or to highly concentrated light beams, especially laser beams. Mechanical application of holes by puncturing the envelopes or removal of material of the envelopes (i.e., burning of holes into the envelopes) is carried out in such a way that the combined cross-sectional area of all holes in each of a series of tubular envelopes equals to closely approximates a desired value. Such mode of ventilating the envelopes of cigarettes or like products is not entirely satisfactory because the rate at which cool atmospheric air can flow into the interior of a lighted cigarette depends on a number of variable parameters, i.e., the application of holes whose combined cross-sectional area matches or approximates a predetermined cross-sectional area cannot invariably insure the admission of a certain optimum quantity of cool atmospheric air into the column of tobacco smoke which flows within the envelope from the lighted end toward and into the smoker's mouth.
Methods and apparatus for making holes in the envelopes of rod-shaped products are disclosed, among others, in commonly owned U.S. Pat. No. 4,090,826 granted May 23, 1978 to Alfred Hinzmann and U.S. Pat. No. 4,121,595 granted Oct. 24, 1978 to Uwe Heitmann et al on application Ser. No. 766,927 filed Feb. 9, 1977 now U.S. Pat. No. 4,118,735 as in commonly owned copending applications Ser. Nos. 841,108 filed Oct. 11, 1977, now U.S. Pat. No. 4,193,409 by Gunter Wahle et al., 805,712 filed June 13, 1977 by Uwe Heitmann et al. now abandoned and 864,441 filed Dec. 1977 by Elke Luders et al.